1. Field of the Invention
The present disclosure relates to a method of detecting impurities in a high-temperature aqueous solution and an apparatus of detecting impurities for the same.
2. Description of the Related Art
It has been known that one of principal causes of damages or failures of pressure vessels, heat exchange pipes, water supply pipes and turbines that are important in wholesomeness and economic feasibility of high temperature energy systems such as nuclear power plants or thermoelectric power plants comes from corrosion phenomena generated by cooling water at high temperatures and high pressures. A dissociation constant of water is increased, and an activity of chemical species causing the corrosion is also increased at high temperatures to accelerate corrosion of metals. Accordingly, metallic structure material brought into contact with high-temperature cooling water is exposed to a high corrosion environment. Therefore, stainless steel or special alloy with high corrosion resistance is generally used as the metallic structure material. However, even although the above-mentioned stainless steel with high corrosion resistance is used, there is a problem that local corrosion such as pitting is progressed even in an alloy such as stainless steel in an environment with highly corrosive chemical species such as chloride ions. Therefore, limitation values of the concentration for such chemical species causing corrosion are being strictly controlled. However, a method of detecting harmful chemical species including anionic chemical species such as chloride ions in real-time without sampling in the state of high-temperature cooling water has not been developed yet.
Currently, conventional analysis methods for detecting chloride ions may include an ion chromatography method and a method of using an ion-selective electrode. A technology of simultaneously measuring boric acid and chloride ions of cooling water in a nuclear power plant by an ion chromatography method is reported in U.S. Pat. No. 4,699,718. Additionally, Passell has developed a system of monitoring quality of cooling water using an on-line chromatography (J. Chromatography A, 671 (1-2), pp. 331-337, 1994), and Reden, et al. have reported a method of measuring the anions in real-time using a chromatography system which is capable of measuring anions through on-line (Faelleskemikerne, Power plant chemical technology, Denmark, 1996. P. 14.1-14.15).
Furthermore, Moskvin, et al. has reported a method of measuring in real-time the concentration of chloride ions in cooling water using an ion-selective electrode (Atomnaya Ehnergiya, USSR. March 1975. V. 38(3) p. 143-145), and Sekeka, et al. has also reported a method of measuring the concentration of chloride ions up to a concentration range of 0.05 to 3.5 ppm in cooling water of heavy-water reactor (CANDU) type nuclear power plant using an ion-selective electrode (J. the Association of Official Analytical Chemists, USA. May 1977. V. 60(3) p. 625-627). Florence has also reported on a technology of measuring the concentration of chloride ions using an ion-selective electrode (J. Electroanalytical Chemistry, 31 (1), pp. 77-86, 1971). However, the foregoing conventional methods are methods that are capable of being applied only in room temperature, and have a limitation that they cannot be applied to an aqueous solution at high temperatures.
On the other hand, Korean Patent Laid-open Publication No. 2009-0083073 has reported a method of detecting the existence of chloride ions using a platinum electrode at high temperatures. However, the foregoing method is based on a technology of measuring a difference in oxidation currents of dissolved hydrogen under the steady state simply when passing dissolved hydrogen through the noble metal oxide film with different porosities by using a porosity difference of noble metal oxide films formed according to the concentration of chloride ions. Therefore, the foregoing method has a limitation that there is a difficulty in detecting chloride ions of low concentration although the method is capable of being applied to high temperature conditions of an aqueous solution.
Thus, the present inventors have developed an original technology capable of measuring the concentration of chloride ions from a transition that oxidation current decreases according to application time of electrochemical potential based on the fact that growth rate of a platinum oxide film is influenced by the concentration of chloride ions when the platinum oxide film is moved by an electrochemical potential produced instead of the oxidation current difference under the steady state by using an electrode of noble metal such as platinum, thereby leading to completion of the present invention.